The invention relates to fuel injection volume correction control for an internal combustion engine and, in particular, relates to improvement in reliability and stability of correction in fuel microinjection volume correction control, and the like.
How to execute fuel injection control in an internal combustion engine is an essential matter as it significantly influences operation performance of the internal combustion engine. As it has been well known, various control methods therefor have conventionally been proposed and in practical use.
For example, there is a well-known technique of performing pilot injection at multiple stages in a diesel engine in order to achieve moderate combustion for reduced engine vibrations during combustion, improve fuel consumption, and reduce pollutants in exhaust gas.
In order to sufficiently and reliably exert effects of such pilot injection as described above, it is necessary to accurately control a microinjection volume therefor. However, injection characteristics vary by fuel injection valves due to manufacturing tolerances, deterioration by aging, and the like, and thus a deviation of an actual injection volume from an instructed injection volume is inevitable.
In order to eliminate the deviation in the fuel injection volume, just as described, it is common to execute correction control of the injection volume in pilot injection control.
As a known technique of correcting such a pilot injection volume, for example, in a state where an accelerator pedal is not depressed, microinjection is performed when a vehicle is in a non-injection state, a fluctuation amount of an engine speed at the time is detected, the fuel injection volume that is considered to be actually injected by the fuel injection valve is calculated on the basis of the detected fluctuation amount of the engine speed, and the fuel injection volume is corrected using a difference between the calculation result and the instructed injection volume as a correction volume of the fuel injection volume for the pilot injection (for example, see JP-A-2011-256839 and the like).
In the above-described fuel injection volume correction method, the fluctuation amount of the engine speed that is acquired by the microinjection is extracted on the basis of a rotation signal acquired by a sensor that detects rotation of a crankshaft of the engine. Thus, as long as the microinjection volume is the same, the fluctuation amount of the engine speed normally remains constant regardless of a gear shift operation of a transmission. However, in reality, it has been known that the fluctuation amount of the engine speed changes in accordance with a gear stage and the engine speed during travel.
For this reason, a method of eliminating an influence of the transmission as described above by calculating a correction coefficient that corresponds to the gear stage and the engine speed by using a map that is defined in advance on the basis of a test or the like and correcting the fluctuation amount of the engine speed resulting from the operation of the transmission by the correction coefficient has conventionally been adopted.
In recent years, in order to handle requests of diversified vehicle models and the like, for example, a diesel vehicle on which a mechanical transmission has conventionally and frequently been mounted is configured by including a continuously variable transmission, and such a vehicle with the configuration and the like have been commercialized.
In the case where the above fuel injection volume correction control is applied to such a vehicle using the continuously variable transmission, instead of the gear stage, which has conventionally been used, a gear ratio is used for the fuel injection volume correction control by a control device that executes operation control of the continuously variable transmission (hereinafter referred to as a “continuously variable transmission control device” for convenience of the description).
Thus, it is necessary to convert the input gear ratio to the gear stage that corresponds to the gear ratio and retrieve the correction coefficient from the above map.